Adsorption of chloroacetanilide herbicides on Hungarian soils

Abstract

Acetochlor and propisochlor are chloroacetanilide herbicides that are produced in Hungary. Their prolonged use in agriculture can result in soil contamination. The study of adsorption on different soil types helps predict the fate of these compounds in the environment. Static equilibrium experiments were carried out with Hungarian soils having different pH and humus content (chernozem, brown forest and sandy soil) in 0.1 mol/1 phosphate buffer (pH 7). The concentration of chloroacetanilide herbicides was measured by high-performance liquid chromatography in the aqueous phase. The amount of the compound adsorbed on a unit mass of the soils is higher in the case of propisochlor than in the case of acetochlor. The difference between the amounts bonded to chernozem and sandy soil is small. As propisochlor is more hydrophobic than acetochlor, and chernozem has the highest organic content, these results support the idea of hydrophobic interaction between the compounds studied and the soil constituents but it can be explained by the formation of hydrogen bonding as well. The resulting adsorption isotherms consist of two parts that can be assigned to two different Langmuir-type isotherms. This phenomenon can be explained by two causes: either by the two phases of the soils (organic and inorganic phases) or by the interaction of the dissolved material with the first monomolecular layer.